Wood conditioning process



Patented Dec. 19, 1950 WOOD CONDITIONING PROCESS William P. Hoffman, Buffalo, N. Y.

N Drawing. Application April 21, 1947, Serial No. 742,97 3

3 Claims.

This invention relates to a wood conditioning process.

In the treatment of wood, particularly for interior finishes, furniture, cabinets, or like articles, the wood is roughly cut to predetermined sizes and is then subject to either the air drying step, or to the step of kiln drying. In the air or natural drying process, the time runs from two to five years, whereas in the kiln process the time is reduced to a matter of three weeks or more, depending upon the moisture and sap content of the wood, and upon the thickness of the boards. However, in each of these processes a great number of checks or cracks develop and the wood warps, with the result that a very substantial amount of wood must be considered useless, and where warps occur, ample allowance must be made so that finished or planed boards of the desired thickness may be obtained.

It is an object of this invention to provide an improved process for conditioning or treating wood which will eliminate almost all checks or cracks, and will reduce warping to the minimum.

Another object of this invention is to provide an improved process for conditioning wood which will very materially speed up the drying period in any of the present drying processes, and at the same time will produce a greater percentage of useable lumber than is possible by present processes or apparatus.

A further object of this invention is to provide an improved process for conditioning wood which can be used for all kinds of wood, and for all sizes of wood, and can be used for wood which has been reshly cut or which has been cut for any period of time before being subjected to the drying process.

In the carrying out of this process, the wood is subjected to a freezing temperature in a closed chamber. The freezing temperature will vary according to the wood structure and the wood sizes. The freezing temperature may vary within a fairly wide range and may be from F. to -5 F., more or less.

The time period within which the wood is subjected to the freezing temperature will also vary within quite a wide range, depending upon whether the wood is hard or soft, and of either close or fine grain, and also depending upon the thickness of the wood. The freezing time may vary from 12 to 60 hours, more or less.

The wood is subjected to the freezing temperature a sufficient length of time until the frost penetrates entirely into the wood so that a crosscut through the frozen wood will show that all of the sap and other moisture in the wood has been frozen. This freezing of the wood effects an expansion of the sap and moisture to a point where the cell linings are ruptured.

After the wood has been thoroughly frozen, it may be put through either an air drying process or a kiln drying process. In the kiln process the wood is subjected to a drying heat for a predetermined time period, and as the cellular structure of the wood has been broken by the quick freezing step, the heat will be able to more quickly penetrate into the wood, and the sap or other moisture will flow from the broken cells to the wood surface where it will quickly dry.

The apparatus for effecting freezing of the wood may be either in a chamber separate from the drying chamber, or may be in the same chamber. When the freezing apparatus is in the same chamber as the drying apparatus, the latter is rendered inoperative during the initial freezing step, and the freezing apparatus is rendered inoperative during the drying step.

As a practical example, it may be stated that a board of freshly cut red oak one-half inch thick by three inches wide, was placed in a freezing temperature of not lower than -5 F. This piece of wood was maintained in the freezer for a period of twelve hours, after which a cut was made across the wood and the cellular structure closely examined. The sap and other moisture in the wood was frozen solid. This initially frozen piece of wood was then dried under heat, and at the same time a piece of wood from the same tree and of the same thickness was heat treated. The piece of wood which was first frozen came out of the heat drying process in substantially perfect condition, that is free from warpage and checks or cracks, Whereas the unfrozen piece came out of the drying process with a number of checks or cracks and was also substantially warped. Furthermore, during the drying process, the pieces of wood were weighed and at each weighing the frozen piece weighed less than the unfrozen piece, thereby showing a quicker sap and moisture evaporation.

It appears from experiments which have been made up to this time that the degrees of temperature and the time of exposure of the wood to the freezing temperature are not critical, and will depend in great measure upon the kind and. thickness of the wood in addition to the time which elapsed from initial cutting of the wood to the start of the freezing step.

Under this process there will not be any case hardening of the wood which occurs in prior drying methods. The cellular structure of the wood being ruptured, the sap and moisture flow will begin when the wood surface gets warm, even though the interior of the wood may be still frozen.

It is my theory that the freezing of the wood causes the cell linings to be ruptured. However, whether or not thecell linings are actually ruptured, the efiect obtained is the desirable effect as hereinbefore set forth.

It will be understood that the term wood as used herein includes especially cut lumber.

What I claim is:

1. A wood drying process which includes the steps of placing a predetermined quantity of cut wood in a closed compartment, refrigerating the compartment to a temperature range of substantially 10 F. to 5 F. thus quick freezin the sap and moisture contained in the cellular structure of said wood, continuing said freezing temperature for substantially 12 hours to solidly freeze said sap and moisture to thereby rupture the cellular structure of the wood, removing the wood from the compartment and placing it in another compartment and substantially immediately thereafter applying heat to the second compartment for a suificient time to melt the ice formed in the wood and to evaporate the liquid formed as the ice melts, and continuing the heating operation until the wood is kiln dried.

2. A wood drying process comprising placing a predetermined quantity of cut wood in a closed compartment, refrigerating the compartment to lower the temperature of the wood to a range of substantially 10 F. to -5 F. thus quick freezing the sap and moisture contained in the cellular structure of said wood, continuing said freezing temperature for substantially 12 hours to solidly freeze said sap and moisture to rupture the cellular structure of the wood, discontinuing the refrigeration operation and substantially immediately thereafer applying heat to the wood for a suificient time to melt the ice formed therein and to evaporate the liquid formed as the ice melts, and continuing the heating operation until the wood is kiln dried.

3. A wood drying process comprising placing a predetermined quantity of cut wood in a closed compartment, mechanically refrigerating the compartment to lower the temperature of the wood to a temperature to thoroughly freeze the sap and moisture contained in the cellular structure of said wood, continuing said freezing temperature for a sufficient length of time to solidly freeze said sap and moisture to effect rupturing of the cellular structure of the wood, discontinuing the refrigeration operation and thereafter applying heat to the wood for a sufficient time to melt the ice formed therein and to evaporate the liquid formed as the ice melts, and continuing the heating operation until the wood is kiln dried.

WILLIAM P. HOFFMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,968,910 Poole Aug. 7, 1934 2,028,296 Shoemaker Jan. 21, 1936 2,146,902 Martin Feb. 14, 1939 2,333,850 Dunkley Nov. 9, 1943 2,368,811 Einersson Feb. 6, 1945 

1. A WOOD DRYING PROCESS WHICH INCLUDES THE STEPS OF PLACING A PREDETERMINED QUANTITY OF CUT WOOD IN A CLOSED COMPARTMENT, REFRIGERATING THE COMPARTMENT TO A TEMPERATURE RANGE OF SUBSTANTIALLY 10*F TO -5*F. THUS QUICK FREEZING THE SAP AND MOISTURE CONTAINED IN THE CELLULAR STRUCTURE OF SAID WOOD, CONTINUING SAID FREEZING TEMPERATURE FOR SUBSTANTIALLY 12 HOURS TO SOLIDLY FREEZE SAID SAP AND MOSITURE TO THEREBY RUPTURE THE CELLULAR STRUCTURE OF THE WOOD, REMOVING THE WOOD FROM THE COMPARTMENT AND PLACING IT IN ANOTHER COMPARTMENT AND SUBSTANTIALLY IMMEDIATELY THEREAFTER APPLYING HEAT TO THE SECOND COMPARTMENT FOR A SUFFICIENT TIME TO MELT THE ICE FORMED IN THE WOOD AND TO EVAPORATE THE LIQUID FORMED AS THE ICE MELTS, AND CONTINUING THE HEATING OPERATION UNTIL THE WOOD IS KILN DRIED. 